Two aspects of the regulation of myocardial energy generation will be investigated in the proposed research. A study will be made of the mechanism and the effectiveness of GTP as a regulator of various cellular enzymatic processes. The inhibitory effects of GTP on the mitochondrial alpha-ketoglutarate dehydrogenase complex will be delineated both at the level of the purified enzyme derived from heart tissue and at the level of the intact cardiac mitochondrion. A mechanism for the GTP-mediated inhibition of the transfer of reducing equivalents from NAD-linked substrates to the NADH level of the electron transport chain will be investigated relative to the activity of the dihydrolipoyl dehydrogenase flavoprotein. Evidence will be sought linking the effects of GTP on mitochondrial electron transport and energy generation with the GTP-mediated coupling mechanism between the catecholamine and polypeptide hormone receptors and the adenyl cyclase of the plasma membrane. This aspect of the proposed research will be designed to define the integrated regulatory relationships between GTP- mediated processes at the levels of the plasma membrane, the cytosol (protein synthesis and gluconeogenesis) and the mitochondrial compartment of the cell. The second aspect of the proposed research involves the elucidation of magnesium-mediated control mechanisms in cardiac tissue. The presence of magnesium binding sites on subcellular membranes will be studied in cardiac tissue. The energy dependence, the effects of a variety of effector molecules and the specificity of magnesium binding and release will be considered. An attempt will be made to characterize a possible magnesium binding factor constituent in cellular membranes which may serve as a reservoir for magnesium which may be alternately released or sequestered depending upon the energetic requirements of the tissue. It is proposed to elucidate membrane associated enzyme systems which may be regulated by changes in the ratio of bound/free magnesium within subcellular organelles. (e.g. the ketoacid oxidases, succinate dehydrogenase, electron transport enzymes or the oxidative phosphorylation sequence). The significance of this research derives from the importance to elucidate the integrate regulatory mechanisms involved in the life sustaining, energy generating function of myocardial tissue.